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drivers: bluetooth: hci: spi: add small read delay

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Add a small delay between reading the transport header and reading the
HCI data. Failing to do so on a nRF9160<->nRF52832 link was reliably
resulting in the nRF9160 trying to read data before the nRF52832 had
set up the SPI transaction, resulting in the host reading a buffer full
of 0x00 and having to run the entire read result again.

Transceiving a 10 byte packet takes at least 31uS, while 100 byte
packets are around 150uS (duration of `spi_transceive` call). Waiting
1 tick to eliminate the need for most retransmissions is a valid
tradeoff.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>
This commit is contained in:
Jordan Yates 2023-06-16 13:20:02 +10:00 committed by Carles Cufí
parent 21ed808ba1
commit b3f12b430f
2 changed files with 23 additions and 0 deletions
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11
drivers/bluetooth/hci/spi.c
View file

@ -56,6 +56,8 @@ LOG_MODULE_REGISTER(bt_driver);
*/
#define SPI_MAX_MSG_LEN 255 /* As defined by X-NUCLEO-IDB04A1 BSP */
#define DATA_DELAY_US DT_INST_PROP(0, controller_data_delay_us)
static uint8_t rxmsg[SPI_MAX_MSG_LEN];
static uint8_t txmsg[SPI_MAX_MSG_LEN];
@ -326,11 +328,20 @@ static void bt_spi_rx_thread(void)
header_slave[STATUS_HEADER_TOREAD] == 0xFF) &&
!ret)) && exit_irq_high_loop());
/* Delay here is rounded up to next tick */
k_sleep(K_USEC(DATA_DELAY_US));
size = header_slave[STATUS_HEADER_TOREAD];
if (ret == 0 && size != 0) {
do {
ret = bt_spi_transceive(&txmsg, size,
&rxmsg, size);
if (rxmsg[0] == 0U) {
/* Consider increasing controller-data-delay-us
* if this message is extremely common.
*/
LOG_DBG("Controller not ready for SPI transaction "
"of %d bytes", size);
}
} while (rxmsg[0] == 0U && ret == 0);
}

12
dts/bindings/bluetooth/zephyr,bt-hci-spi.yaml
View file

@ -23,3 +23,15 @@ properties:
description:
Minimum duration to hold the reset-gpios pin low for.
If not specified no delay beyond the code path execution time is guaranteed.
controller-data-delay-us:
type: int
default: 20
description:
Duration to delay between reading a valid header and reading the data associated
with that header. This delay gives the controller time to configure the SPI data
transaction after finishing the header transaction. Without this delay the host
can attempt to read before the controller is ready, resulting in empty data that
then needs to be read a second time. The default of 20uS was chosen as the lowest
delay that reliably eliminated double transmits between a nRF9160 host and a
nRF52832 controller.